1. Field of the Invention
The present invention relates to a gas turbine and, more particularly, to supporting legs of a casing of a gas turbine.
2. Description of the Related Art
A gas turbine compresses air by a compressor into high-temperature, high-pressure compressed air, and supplies a fuel to this compressed air in a combustor, where the fuel is burned to generate a high-temperature, high-pressure combustion gas. This high-temperature, high-pressure gas is fed into a turbine and the expansion of this high-temperature, high-pressure gas in the turbine causes a main shaft to rotate so as to drive a generator or the like.
In a casing that forms an outer shell of such a gas turbine, thermal deformation due to the heat of internal compressed air and combustion gas and deformation due to inner pressure occurs axially and radially. In order to absorb this axial and radial deformation of the casing, there has hitherto been used a construction which is such that the casing is fixedly supported on the side of one axial end and supported in a displaceable manner on the side of the other end.
For example, in Japanese Utility Model Laid-Open No. 60-10838, as a construction in which the side of the other end of the casing is supported in a displaceable manner, a supporting leg that supports the side of the other end of the casing is slidable along an inclined surface.
There is also a construction as shown in FIG. 4. A casing 2 of a gas turbine 1 is supported, on the compressor 3 side, by a fixed supporting leg 5 that is fixed on a foundation 4, and on a turbine 6 side, by a movable supporting leg 7 that allows the deformation of the casing 2. As shown in FIG. 5, the movable supporting leg 7 is composed of link plates 8 provided on both sides of the casing 2 and a supporting member 9 provided below the casing 2.
The link plate 8 is provided perpendicularly to the foundation 4 in a stop condition of the gas turbine 1, and upper and lower parts thereof are rotatably connected to the casing 2 and the foundation 4, respectively, by pins 8a, 8b. As a result of this, when the casing 2 is axially deformed, the link plate 8 rotates relatively, in the parts of the pins 8a, 8b, with respect to the casing 2 and the foundation 4, and the link plate 8 inclines in a tilting direction, with the pin 8b in the bottom end part serving as the center. This allows axial deformation of the casing 2.
This link plate 8 itself undergoes lateral elastic deformation in FIG. 5, whereby this link plate 8 supports the casing 2 by allowing the radial deformation of the casing 2.
The supporting member 9 allows vertical displacement of the casing 2 while constraining the casing 2 laterally (laterally in the cross-section of the casing 2).
This supporting member 9 is such that a bottomed cylindrical sleeve 9b is integrally provided on the side of one end of a shaft 9a and a sleeve 9c of the same shape is integrally provided on the side of the other end. A lower part of the casing 2 is bonded to the sleeve 9b and the sleeve 9c is fixed to the foundation 4 side. The inside diameter of the sleeves 9b, 9c is larger than the diameter of the shaft 9a, and a clearance is formed between an inner circumferential surface of the sleeves 9b, 9c and an outer circumferential surface of the shaft 9a. Also, a clearance is formed between the sleeve 9b and the sleeve 9c so that the two do not come into contact with each other.
According to such a supporting member 9, when the gap between the foundation 4 and the casing 2 displaces due to radial deformation of the casing 2 and a swing of the casing 2, the shaft 9a undergoes elastic deformation and the sleeves 9b, 9c are relatively displaced vertically. This enables the radial deformation of the casing 2 and the vertical swing of the casing 2 to be absorbed. The shaft 9a is less apt to be axially deformed compared to the elastic deformation of the shaft 9a occurring at this time and, therefore, the casing 2 is laterally constrained.
The casing 2 of the gas turbine 1 is divided into two parts of an upper casing 2a and a lower casing 2b. In the supporting construction using the link plate 8, in order to ensure connecting strength of the link plate 8 to the lower casing 2b, a thick-walled portion 11 is formed below a top surface of the lower casing 2b and a top end portion of the link plate 8 is connected to the lower casing 2b by the pin 8a. For this reason, the top end portion of the link plate 8 is offset below the mating faces of the upper casing 2a and the lower casing 2b, i.e., the central axis C of a main shaft 10.
In such a construction, the radial deformation of the lower casing 2b occurs between the top end portion of the link plate 8 (the part connected to the lower casing 2b by the pin 8a) and the top surface of the lower casing 2b as well. For this reason, when the operation status of the gas turbine 1 shifts from a stop condition to an operating condition and the temperature of the casing 2 rises, the central axis C of the main shaft 10 is displaced upward with respect to the foundation 4 as shown in FIG. 6.
At this time, within the gas turbine 1, the temperature and pressure of the internal air rise from the compressor 3 side toward the turbine 6 side and also the amount of deformation occurring in the casing 2 becomes more remarkable on the turbine 6 side than on the compressor 3 side. For this reason, the position of the central axis C of the main shaft 10 becomes higher on the turbine 6 side, which is supported by the movable supporting leg 7, than on the compressor 3 side, which is supported by the fixed supporting leg 5. As a result, a bending stress acts on the main shaft 10. This bending stress results in repeated stressing of the main shaft 10 in the tension and compression directions as the main shaft 10 rotates, and has an effect on the durability of the main shaft 10.
The present invention has been accomplished on the basis of such a technical challenge and has as its object the provision of a gas turbine capable of improving the durability of a main shaft by absorbing the deformation of a casing due to heat and pressure and suppressing stresses acting on the main shaft.